1. Field of the Invention
Embodiments of the present invention generally relate to a process of reliably forming devices on a semiconductor substrate.
2. Description of the Related Art
Currently, copper and its alloys are the metals of choice for sub-micron interconnect technology because copper (Cu) has a low resistivity, a high current carrying capacity, and high electromigration resistance. However, despite the positive attributes of Cu, Cu interconnects are susceptible to copper diffusion, electromigration related failures, and oxidation related failures. Typically, a liner barrier layer is used to encapsulate the sides and bottom of the Cu interconnect to prevent diffusion of Cu to the adjacent dielectric layers. The oxidation and electromigration related failures of Cu interconnects can be significantly reduced by depositing a thin metal capping layer of, for example, cobalt tungsten phosphorus (CoWP), cobalt tin phosphorus (CoSnP), and cobalt tungsten phosphorus boron (CoWPB), on the surface of the Cu interconnect. After depositing a capping layer and subsequent dielectric layers, high processing temperatures reaching 400° C. to 450° C. for periods of about 8 hours during back-end-of-the-line (BEOL) layer processing and chip packaging leads to delamination of the subsequently deposited dielectric layers from the capping layer if adhesion between the capping layer and dielectric layer is poor. Lags in the processing sequence may also encourage oxidation. In particular, oxidation is particularly detrimental in thinner capping layers having thicknesses of less than about 150 Å, for example, a 70 Å layer of CoWP or CoWPB. Increasing adhesion and decreasing the concentration of oxides across the surface of the deposited capping layer over the Cu interconnect is needed to prevent delamination of the subsequently deposited dielectric layers.
FIG. 1 (prior art) is a sectional view of a formed feature. The feature is formed on a substrate surface 11. A dielectric layer 14 is deposited on the substrate 11. A via 10 is formed in the dielectric layer 14. A barrier layer 12 is deposited in the via 10. Copper or other conductive material 13 is deposited on the barrier layer 12. The conductive material 13 is then planarized and a capping layer 22 is deposited on the conductive material 13. Next, a dielectric layer 16 with a low dielectric constant is deposited on the dielectric layer 14 and the capping layer 22. An interface 17 is formed between the capping layer 22 and the dielectric layer 16. Then, an additional dielectric layer 18 is deposited. The additional dielectric layer may be fluorosilicate glass (FSG), amorphous silicon, silicon oxycarbide, or other dielectric selected for its dielectric constant or other properties. The dielectric layers 18 and 16 may be one continuous dielectric layer composite 15. Next, a photoresist is deposited upon the surface of the dielectric layer 18. The photoresist is patterned and the underlying dielectric composite 15 is also patterned. As the dielectric layer 16 is patterned, the interface 17 between the capping layer 22 and dielectric layer 16 may lose integrity and deform. Specifically, if there is limited adhesion between the capping layer 22 and the dielectric layer 16, the capping layer 22 and dielectric layer 16 may delaminate, leading to device failure.
Historically, the capping layer has been deposited, quickly followed by depositing the dielectric layer. FIG. 7 (prior art) illustrates a process 50 for depositing a low dielectric constant film on the capping layer. The substrate is preheated in an oxygen containing environment in step 51. Next, a silicon containing precursor such as silane or tetraethyl orthosilicate (Si(OC2H5)4, tetraethyloxysilane, or TEOS) is introduced into the chamber in step 52. Then, the plasma is ignited in step 53. The bulk dielectric layer is deposited in step 54. Because capping layer 22 is susceptible to oxidation, the above process 50 results in oxidation of the capping layer 22 and poor adhesion between the capping layer 22 and low K dielectric layer.
Improved methods and apparatus are needed to deposit and treat a capping layer to increase the adhesion between a capping layer and a dielectric layer. The improved method and apparatus may provide a capping layer with improved copper diffusion barrier properties. The improved copper diffusion barrier may also be an etch stop. Thus, the dielectric capping layer, such as layer 16, may be eliminated from the process, and a low K dielectric may be deposited directly on the capping layer.